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The study investigated methane production from dehydrated waste-activated sludge (DWAS) with approximately 80% water content under thermophilic conditions. The repeated batch-wise treatment of DWAS using methanogenic sludge unacclimated to high concentrations of ammonia, increased the ammonia production up to 7,600 mg N per kilogram total wet sludge of total ammonia concentration, and stopped the methane production. Investigation revealed that the loading ratio of DWAS for methanogenic sludge influences anaerobic digestion. Methane production significantly decreased and ammonia concentration increased with the increase in loading ratio of DWAS. Since the semicontinuous culture revealed that approximately 50% of organic nitrogen in DWAS converted to ammonia at sludge retention time (SRT) after 4 days at 37 degrees C and 1.33 days at 55 degrees C, the previous stripping of the ammonia produced from DWAS was carried out. The stripping of ammonia increased methane production significantly. This ammonia-methane two-stage anaerobic digestion demonstrated a successful methane production at SRT 20 days in the semicontinuous operation using a laboratory-scale reactor system.

This study tested the effect on thermophilic and mesophilic digestion of poultry manure (PM) or treated poultry manure (TPM) by the addition of agriculture wastes (AWS) as a co-substrate under dry conditions. PM was co-digested with a mixture of AWS consisting of coconut waste, cassava waste, and coffee grounds. Results were increased methane content in biogas, with decreased ammonia accumulation and volatile acids. The highest performance occurred under mesophilic conditions, with a 63 and 41.3 % increase in methane production from addition of AWS to TPM (562 vs. 344 mL g VS(-1) from control) and PM (406 vs. 287 mL g VS(-1) from control), respectively. Thermophilic conditions showed lower performance than mesophilic conditions. Addition of AWS increased methane production by 150 and 69.6 % from PM (323.4 vs. 129 mL g VS(-1) from control) and TPM (297.6 vs. 175.5 mL g VS(-1) from control), respectively. In all experiments, 100 % acetate produced was degraded to methane. Maximum ammonia accumulation was lowered to 43.7 % by mixing of AWS (range 5.35-8.55 vs. 7.81-12.28 g N kg(-1) bed). The pH was held at 7.3-8.8, a range suitable for methanogenesis.